This application is based on application No. 11-93009 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an information display device and a display control method, and more particularly to an information display device which has a display with a memory effect and a display control method adopted in the device.
2. Description of Related Art
At present, information is widely distributed by use of printed matter; it, however, increases the volume of garbage and promotes exhaustion of forest resource for paper pulp. These problems can be eased by developing a system of providing information being stored in digital information storage media so that users can get the information by use of display devices such as liquid crystal displays, electro luminescent displays, plasma display panels, etc. For example, various kinds of information which have been conventionally distributed by printed matter, such as books (paperbacks, weekly magazines, monthly magazines, technical papers, etc.), newspapers and advertisements can be distributed in the above-described way by an electronic book system.
Publishers (makers) distribute digital information of books as storage media to users which have (own or rent) a display device of an electronic book system, and each user puts the storage media in the display device to get the information.
In order to attain such a system, the display device must be as small and thin as a book so that the user can use it anywhere. It is, therefore, necessary to use a display with a memory effect which consumes little electric power, which requires a power source section of only a small size such as a dry battery, a small battery, a small capacitor or the like.
When such a power source section is used up, for example, when the battery comes to the end of its life, the image displayed on the display will stay thereon, which may cause trouble. For example, if the power source is used up while secret information is displayed on the display, the information will not be able to be erased until a new battery is loaded or until the power source section is recharged.
An object of the present invention is to provide an information display device which is capable of erasing an image from a display even when its power source section is used up and a display control method adapted in the display device.
Another object of the present invention is to provide an information display device which displays an image on a display without being influenced by the previous state of the display immediately after its power source section is recharged.
In order to attain the objects above, an information display device according to the present invention comprises: a display section which has a screen made of a material with a memory effect; a power source section which supplies electric power; a detecting section which detects a voltage supplied from the power source section; an erasure mode selecting member with which a user selects an erasure mode to erase the screen; and a control section which executes the erasure mode on conditions that the erasure mode is selected and that the voltage detected by the detecting section is not more than a specified voltage.
According to the present invention, immediately before the electric power of the power source section is used up, the information displayed on the screen is erased. Accordingly, there is no fear that the display may keep displaying secret information on the screen. There are cases wherein this erasure mode is not necessary, and for this reason, the erasure mode selecting member with which a user can select and cancel the erasure mode is provided. It is preferred that the selection or cancellation of the erasure mode is maintained even after recharge of the power source section. This arrangement eliminates the user""s trouble of setting the erasure mode again after recharge of the power source section.
In the information display device according to the present invention, skip erasure to erase the screen while skipping pixels at intervals may be performed. If the skip erasure is performed in such a way to make the displayed information unrecognizable by other people, although the information is not completely erased, the secrecy is kept while less electric power is necessary for the erasure. For the same purpose, only part of the screen may be erased.
If the remaining electric power of the power source section is displayed on the screen, the user can recognize the exhaustion of the power source section and can prepare for recharge.
If the display section has a plurality of screens and if all the screens are subjected to operation in the erasure mode, execution of the erasure mode requires a large amount of electric power, and electric power which can be used for ordinary use of the information display device is reduced. In order to avoid the trouble, selection of at least one screen as the object of the erasure mode shall be possible. The control section figures out the number of screens which are capable of being erased in the erasure mode based on the remaining electric power. If the control section judges that the erasure mode cannot be executed toward all the screens, the control section issues a warning, or automatically selects at least one from the screens and erases only the selected screen. The selection of one or more screens as the object of the erasure mode may be made by the user.
The information display device according to the present invention may erase the screen also when the power source section is recharged. Since the display section uses a material with a memory effect, the display performance is influenced by the previous display state. For example, if a new image is written on the screen over an image displayed thereon, the contrast of the newly written image becomes uneven. In order to avoid such trouble, the screen is reset immediately after recharge of the power source section, and thereafter, a new image is written thereon. Thereby, an image of a high quality can be displayed.